Regular Expressions 101

^start of line

Character Class[a-zA-Z\d]+

+matches at least one character from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\da digit

Positive Lookahead(?=([-_])?)

Group 1([-_])?

?repeats the group contents below at most once:

Character Class[-_]

-the literal - (45₁₀ / 55₈ / 2D₁₆)

_the literal _ (95₁₀ / 137₈ / 5F₁₆)

Non-Capturing Group(?:\1[a-zA-Z\d]+)*

*repeats the group contents below any number of times:

\1the text saved by group 1

Character Class[a-zA-Z\d]+

+matches at least one character from the set below:

a-zone character from a (97₁₀) to z (122₁₀) (case sensitive)

A-Zone character from A (65₁₀) to Z (90₁₀) (case sensitive)

\da digit

$end of line

Global pattern flags

g modifier: global. Finds all matches instead of stopping after the first

m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string

Detailed match information will be displayed here automatically.

25 tokens

Regular Expression

^[a-zA-Z\d]+(?=([-_])?)(?:\1[a-zA-Z\d]+)*$

New

-test
 : false 
test-
 : false
te--st
 : false
test
 : true
test-test
 : true 
te-st-t
 : true 
te-st_test
 : false
te_st_test
 : true

-test
 : false 
test-
 : false
te--st
 : false
test
 : true
test-test
 : true 
te-st-t
 : true 
te-st_test
 : false
te_st_test
 : true